2. NEED FOR SHADING
When ambient temperatures are within or
above the comfort zone, any ingress of
solar radiation will contribute to discomfort.
Shading design must prevent this.
However, at cool times of the year, it may
be desirable to allow solar radiation to
pass directly into the room, to provide a
useful heating effect. This response can
be provided either by the shading device
moveable or by it being geometrically
selective.
3. FUNCTION OF SHADING
Solar radiation entering a room can have three
effects :
• Radiation absorbed on to room surfaces will lead
to an increase in air temperature.
• Solar radiation falling directly on to an occupant
will lead to an increase in the mean radiant
temperature experienced.
• High intensities of radiation from direct sun or
even the diffused sky can cause discomfort
glare, or disability glare where an occupant’s
visual performance will actually be impaired.
The function of shading is to eliminate
these three effects.
4. FUNCTION OF SHADING
The function of shading is to eliminate
these three effects. i.e.
• to reduce the total amount of radiation
entering the room by reflection and
absorption.
• to improve the distribution of the light in
the room
The functional requirements for shading
change with region and climate.
5. CONSTRAINTS OF SHADING
Shading is itself subject to certain
constraints :
• Maintenance of air flow through the non-
air-conditioned buildings during the cooler
hours of the day.
• There will be a need for admitting
controlled levels of diffused daylight.
• In most cases there will be a requirement
of views out of the window.
6. USE OF SHADING
Solar controls should be considered for all
glazed openings exposed to direct
sunlight. Solar control is particularly
important on south to west-facing facades,
since the solar gains will coincide with the
hottest part of the day. Solar control is
also vital for lightweight buildings with
large areas of glazing.
7. SOLAR SHADING
When sunlight hits a pane of glass, it
splits into three components –
that which is reflected,
that which is absorbed and
that which is transmitted through.
8.
9. SOLAR SHADING
• Reflected component from the glazing has
no thermal effect on the space behind the
glazing.
• Absorbed component within the glazing
itself heats up the glass. Heat is
transmitted inwards and outwards by
conduction and long wave radiation.
• Transmitted component of radiation that
penetrates through the glass raises the
temperature of the surface behind it.
10. SOLAR SHADING
The proportion between the three
components is determined by the angle at
which the solar beam strikes the glazing,
i.e. ‘angle of incident’ and by the type of
glazing.
For most types of glazing, the transmitted
component is very small if the angle of
incidence is larger than 45º from the
normal to the glazing. If the angle is more
than 60º , most of the radiation is
reflected.
11. IMPORTANCE OF SHADING
Use of shading device can improve
building energy performance, prevent
glare, increase useful daylight availability
and create a sense of security. Realizing
these potential benefits, a no. of shading
devices have been invented, such as
fixed, manual and automatic moveable,
internal and external shading device.
12.
13. EXTERIOR SHADING DEVICE
Exterior shading device is primary used
to control the amount of radiation
penetration to the interior of buildings.
Some of them are operable, i.e. they can
be raised or lowered.
Two basic types of exterior shading device
are horizontal and vertical .
14. EXTERIOR SHADING DEVICE
Its effectiveness depends on its type and
placement relative to glass. When
radiation strikes a shading device,
• a part of it is reflected outwards from its
surface,
• another part is reflected onto the glazing
• remaining part is absorbed by itself,
causing it to heat up.
15.
16.
17.
18. INTERIOR SHADING DEVICE
Interior shading devices are mainly
established in order to provide visual comfort by
eliminating glare. Further, interior shading
devices can contribute to the interior
architectural design of rooms without influencing
the exterior façade of the building. Because of
the heat absorption happening inside the
building (the transformation of short wave
sunlight energy into long wave heat energy)
interior shading devices are not as efficient as
exterior shading solutions to reduce solar heat
gains.
19. INTERIOR SHADING DEVICE
Internal shading devices limit the glare
resulting from solar radiation. Internal
shading devices usually are adjustable
and allow occupants to regulate the
amount of direct light entering their space.
Most commonly these take the form of
horizontal or vertical blinds attached
above windows.
20. INTERIOR SHADING DEVICE
In rooms that are oriented north or east without
risk for overheating in the summer, the following
interior shading devices are in use :
• Venetian blinds – horizontal blade construction,
which can be lowered and elevated (1)
• Roller blinds - textile curtains or foils, which are
rolled up above the window (2)
• Pleats curtains – textile curtains, which are
folded above the window (3)
• Vertical-blades - textile vertical blade curtains (4)
• Curtains – textile curtains
23. External Shading
External shading devices are the most efficient
thermally because they intercept the solar
energy before it has entered the room. Its
effectiveness depends on its type and
placement relative to glass. When radiation
strikes a shading device,
• a part of it is reflected outwards from its surface,
• another part is reflected onto the glazing
• remaining part is absorbed by itself, causing it to
heat up.
Thus, even if energy is absorbed by them, it is
not trapped behind the glass. They carry the
disadvantage of having to be weatherproof and
are more difficult to control from inside.
24. Internal Shading
Internal shading is thermally in effective. In such
a case , radiation strikes the glazing with no
interference, penetrating into the internal space,
causing the shading element to heat up, and
from there, heating up the room by both long-
wave radiation and by conduction. Radiation
emitted by the shading device itself is already of
the long-wave type, thus it is trapped by the
glazing in front of it in the same way as any
other long-wave radiation from the interior.
It is generally much cheaper to install and is
easy for users to control, but is less efficient, for
reasons outlined above. It is also vulnerable to
damage.
25.
26. Design Strategy of Shading Devices
The design strategy of the shading device will depend on the
size and orientation of the window openings. Shading devices
can also affect the building appearance. Although the design
of external shading devices involves a number of factors, the
following recommendations are generally applied to all
designs:
• Use fixed overhangs on south-facing glass
• Limit the area of east or west glass. Vertical or egg-crate fixed
shading can be considered if the shading projections are
fairly deep or close together; however these may limit views.
• North-facing glass receives little direct solar gain , usually no
shading is required to this exposure.
• Interior shading devices such as Venetian blinds or vertical
blades do not reduce cooling load since the solar gain has
already been admitted into the indoors. However these
interior devices do offer glare control.
• The durability of shading devices should be considered.
Operable shading devices usually require more maintenance
and repair.
27. Finally, shading and solar control
devices have a great potential for
architectural expression, adding to
the texture and modulation of the
facade. They also have the
potential (and should) respond to
the orientation of the facade, thus
visibly reflecting the building’s place
in the natural world as well as its
urban setting.
28. Vertical & Horizontal Shading Device
Shading devices should be selected
according to the orientation of the window.
• Vertical Shading device is most effective
when sun is to one side of the elevation
and at low angle, such as eastern or
western elevation.
• Horizontal Shading device is most
effective when sun is opposite to the
building face considered and at high
angle, such as for north and south facing
walls.
31. Shadow angles are formed by sun
shading devices or projections on a wall
exposed to the sun. Different design of
sun shading devices form different
shadow angles.
The performance of shading device is
specified by two angles :
• Horizontal shadow angle
• Vertical shadow angle
These angles depend on the position of
the sun and the orientation where the
window is facing.
32. HORIZONTAL SHADOW ANGLE
The horizontal shadow angle (HSA) is
required for (or cast by) vertical shading
devices.
It is the horizontal angle between the
normal of the window pane and the
azimuth of the sun.
HSA = wall azimuth – solar azimuth
33. VERTICAL SHADOW ANGLE
The vertical shadow angle (VSA) is
required for (or cast by) horizontal shading
devices.
It is the angle between the ground line and
altitude of the sun.
34. VERTICAL SHADOW ANGLE
Actually it is measured on a vertical plane
normal to the elevation considered. If we
imagine a virtual plane between the
bottom left-hand and right-hand corners of
the window and the sun, then the VSA is
the angle this plane forms with the ground
plane.
tan VSA = tan(altitude) / cos(HSA)
35.
36.
37. SOLAR ALTITUDE ANGLE &VSA
Solar altitude angle describes sun’s
position in relation to the horizon, while
VSA describes the performance of the
shading device. Numerically, the two
coincide when, the sun is exactly opposite
the wall considered i.e. when solar
azimuth and wall azimuth angle are same
and HSA = 0. For all other cases, when
the sun is sideways from the
perpendicular, the VSA is always larger
than the solar altitude angle.
38.
39. Shade Dimensions
These two angles, HSA and VSA, can
then be used to determine the size of the
shading device required for a window. If
the height value refers to the vertical
distance between the shade and the
window sill, then the depth of the shade
and its width from each side of the
window can be determined using relatively
simple trigonometry.
• Shade Depth : The depth is given by:
depth = height / tan(VSA)
• Shade Width : The width is given by:
width = depth x tan(HSA)
40. Design Requirements
Requirement of shading largely depends upon
the climatic conditions. According to climatic
zones, there are three categories of shading
requirement :
• Complete year round shading
• Complete year round shading but only during
major sunshine hours
• Shading during summer months only
41. Shading Requirements in Different
Climatic Zones
Climatic Zone Requirement
Hot & Dry Complete year round shading
Warm & Humid Complete year round shading but design
should be made such that ventilation is not
affected.
Temperate Complete year round shading but only
during major sunshine hours
Cold & Cloudy No shading
Cold & Sunny Shading during summer months alone
Composite Shading during summer months alone
